The invention relates to a valve needle, in particular to a valve needle used for a spray coating liquid. The invention also relates to valves, apparatus and devices containing at least one valve needle, each for a particular spraycoating liquid.
The German patent documents DE 196 50 781 A1 and DE 196 54 514 A1 show spraycoating apparatus fitted with a valve needle. This valve needle is displaced by compressed gas, preferably compressed air, in one longitudinal direction, and by the force of a compressed spring in the opposite longitudinal direction, so as to act on the plunger of the valve needle. The plunger and the valve needle are integral. High grade steel is used in practice for said integral part. The valve needle wears on account of the liquid rubbing against it and by the friction at the valve-aperture edge.
The object of the present invention is a valve needle comprising an integral shank fitted with a front shank segment constituting the needle tip.
The objective of the present invention is also to extend the service life of the valve needle. Moreover the manufacturing costs shall not be higher than, but rather lower than in the state of the art with respect expenditures for material and processing. Moreover the valve-needle material shall be compatible with the various coating liquids. However the valve needle material also shall be compatible with the valve-seat material, the valve needle in a valve cooperating with the valve seat material. The valve-needle material may not degrade the valve seat material and the service life.
This objective is by the valve needle of the invention which contains an integral shank comprising a front shank-end segment constituting the needle tip, characterized in that a plunger is affixed to the shank, this shank being made of a different material than the piston.
The invention also relates to using such a valve needle and spraycoating apparatus, control units, manifolds and spraycoating devices containing such a valve needle.
The invention offers the following particular advantages: long valve-needle service life due to lesser abrasion of its shank by the coating liquid, in particular at the needle tip; more economical valve-needle manufacturing costs in particular due to the elimination of the constraint that the valve-needle shank must be machined out of a solid material exhibiting the plunger diameter, because the diameter of the plunger used to generate a pneumatic or hydraulic axial valve-needle drive pressure requires a substantially larger diameter than that of the valve-needle shank; the lowered valve-needle manufacturing costs make it more economical to use exchangeable valve needles made of different materials for different spraycoating apparatus and other spraycoating devices in order that there be no chemical reactions between them and the coating liquid; the plunger may be made of a material of lower specific weight than of the needle shank and more economical than said shank""s material, and more easily processed than said shank material.